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passages to be able to mount an immune response
against those antigens that we inhale.
00:01
Let us, first of all, look at the different portions
of the lung. There are two major parts of
the airways, a conducting portion and then
the respiratory portion. Let us, first of
all, look at the conducting portion. In this
slide, on the right-hand side, you see three
images. One is the section through the head
region showing you the oral cavity with the tongue
and the nasal cavity above it. The very circular
like structure down on the bottom right-hand
side of this slide is a section through the
trachea. You can actually feel the trachea
in your neck. You can feel the tracheal cartilages.
You have about 16 to 20 of those cartilages
that are a very important airway going into
the lungs and that is protected by a structure
called the epiglottis. The epiglottis sits
just above the larynx and it also sits right
next to the entry into the esophagus. When
we swallow, if you put your fingers around
your trachea or near your larynx and you swallow,
you can feel the larynx moving upwards. That
closes off the airway during swallowing because
the epiglottis is an elastic cartilage flap
that when you swallow and the larynx is lifted,
it closes off across that epiglottis and so
food then passes down the esophagus, not down
the airways. So that epiglottis is a very
important structure. It is flexible, elastic
cartilage lying mostly by stratified squamous
epithelium because it is wear and tear during swallowing
but also the very small component that sits
just above the larynx entering to the airway
is lined by respiratory tract epithelium.
01:57
We will go to it in more detail later on in
this lecture. Now, the larynx is a structure for
speech production and I will go through that
in more detail at a later time. The bulk of
the upper conducting portion of the airway
consists of the nasal cavity and just at the
back, the nasal pharynx. And if we look
at the nasal cavity just above the area here,
it is important you roughly know at this stage
where it is. You can see a division between
the nasal cavity and the oral cavity that is
the hard palate, and the soft palate towards
the posterior aspect. Well, when air passes down
through the trachea, it passes through another
series of tubes called bronchi. A single bronchus
is labeled here. You can see a couple of them
in this section and also some large blood
vessels. They too are part of the conducting
portion of the respiratory tract and they
will divide as they go deeper down into the lung
into very small units called bronchioles and
that completes the conducting portion of
the lung. Now, the importance of this conducting
portion is firstly to warm the air, and then
to moisten the air, and then to clean
the air of all any inhaled debris we
might happen to inhale into a nasal cavity
and we try to prevent that from getting
down into the lungs. So it is a very important
function of the conducting portion, warm,
moisten and clean the air. Well, here is a couple
of complicated diagrams but I want to just